1. Field of the Invention
The present invention relates to prosthetic devices used for replacement of a natural joint and, more particularly, to prosthetic joints having reduced area bearing surfaces.
2. Background Information
It is known to provide prosthetic joints or joint assemblies for acetabulums, knees, ankles, shoulders, elbows, and wrists. Components of prosthetic joints such as that shown in U.S. Pat. No. 4,068,342 to Townley et al., provide a face having a continuous surface area of articulation for its corresponding member. While conventional prosthetic components beneficially provide a low-friction articular face for the surface of accompanying member, interaction between the articulating component and the member can produce joint debris. Such debris is expelled into the adjacent tissues and may cause adverse reactions in the surrounding bodily tissue.
Attempts have been made to prevent joint debris produced by prosthesis joint assemblies from entering surrounding bodily tissue. See for example, U.S. Pat. No. 4,731,088 to Collier, where a flexible enclosure is applied to a prosthetic joint to isolate the joint debris from the surrounding tissue. It is thus desirable to reduce wear associated with prosthesis joint assemblies.
Prosthesis joint assemblies may be fabricated from various materials. There are hard on hard bearing prosthetic joint assemblies and polyethylene on hard bearing prosthetic joint assemblies. Hard on hard bearing prosthetic joint assemblies or combinations are typically metal-metal or ceramic-ceramic. Polyethylene on hard bearing prosthetic joint assemblies or combinations are typically polyethylene-metal.
For hard-on-hard bearing combinations of an acetabular cup assembly, for example, a lower head to cup clearance (gap) results in lower wear. As well, smaller diameter implants have been associated with lower friction. As implant diameter (head and inner cup with respect to an acetabular cup assembly) increases, the same low clearance for a smaller diameter bearing combination results in a higher contact area for the larger bearing combinations. This results in a higher frictional torque and a reduction in the size of an inlet zone. Excessive reduction in the size of the inlet zone may reduce the potential for lubrication to occur. For polyethylene-on-hard bearing combinations, which have typically been smaller diameter implants, implant wear increases with implant diameter and decreasing clearance. The current trend, however, is towards larger diameter implants.
In view of the above and other considerations, it is an object of the subject invention to provide an improved prosthetic joint.
It is another object of the subject invention to provide an improved joint prosthesis having a surface that minimizes the production of joint debris which can result from articulating movement of the joint prosthesis post implantation.
Another object of the subject invention is to provide an improved prosthetic component of a joint prosthesis having a bearing surface that minimizes the production of joint debris which can result from articulating movement of the prosthetic component post implantation.
Still another object of the subject invention is to provide an improved prosthetic joint that has surfaces that maximizes lubricity in conjunction with a corresponding prosthetic component when implanted in a patient.
A further object of the subject invention is to provide a method of fabricating a prosthetic assembly that has an optimum contact or bearing area.
A still further object of the subject invention is to provide a method of fabricating a prosthetic assembly that has an optimum contact area for a range of prosthetic assembly sizes.